The overall goal of the current proposal is to investigate the novel roles of nicotinamide N- methyltransferase (NNMT) in regulating energy expenditure and adiposity. NNMT catalyzes the S- adenosylmethionine (SAM)-dependent methylation of nicotinamide (vitamin B3), a precursor of nicotinamide adenine dinucleotide (NAD+). NNMT is a unique enzyme in that it regulates both SAM and NAD+, two fundamental metabolites for cellular energy metabolism. SAM provides substrate propylamine for polyamine metabolism and donates a methyl group for histone methylation. Both polyamine metabolism and histone methylation are involved in regulating energy expenditure. NAD+ is a cofactor of Sirt1, a deacetylase that regulates multiple important targets related to energy metabolism. The applicant found that NNMT was elevated in adipose tissue and liver in obesity. Biologically knocking down NNMT in adipose tissue and liver using antisense oligonucleotides (ASO) increased energy expenditure, prevented diet-induced obesity and improved insulin sensitivity. NNMT knockdown increased SAM and NAD+ levels, enhanced polyamine flux and augmented mono-, di- and tri-methylation of lysine 4 on H3 (H3K4) histone methylation in adipose tissue. The overall hypothesis is: NNMT is a novel regulator of energy expenditure and adiposity, and it exerts its effects by causing metabolite shunting leading to changes in cellular SAM and NAD+ levels, which in turn regulate energy expenditure. In Aim 1, we will use pharmacological and genetic approaches to further elucidate the roles of NNMT in regulating energy expenditure. For pharmacological approach, we will use N-methylnicotinamide (MNA), an NNMT feedback inhibitor, to inhibit NNMT activity. For genetic approach, we plan to generate adipose-specific NNMT knockout mice. We will investigate energy expenditure and adiposity in these mice. In Aim 2, we will determine the mechanisms by which alterations in SAM mediate the effects of NNMT on energy expenditure. We will focus on SAM-regulated polyamine metabolism and histone methylation. In Aim 3, we will investigate whether NAD+ and NAD+-dependent Sirt1 are involved in NNMT-regulated energy expenditure. The proposal is highly innovative in the aspects of new discovery, novel mechanisms and comprehensive approaches. It also has significant translational implications. Both NNMT ASOs and MNA can potentially be used directly in clinical trials. In fact, MNA has been used in humans for studying its vasorelaxation effects.